The present invention relates to integrated signal isolators. In particular, the present invention relates to integrated magnetically coupled, single-chip, signal isolators with feedback.
It is known to use extremely small integrated magnetic field sensing devices to sense magnetic fields. Such devices can be made by using a plurality of thin strips or elements of a magnetoresistive film comprising a magnetically responsive material, such as Permalloy(copyright). Magnetization of the film generally forms an angle with the direction of current flow, and the resistance of the film depends on this angle. For example, when magnetization of the film is parallel to the direction of current flow, the resistance of the film is at a maximum. On the other hand, when magnetization is perpendicular to the direction of current flow, the resistance of the film is at a minimum. This phenomena is called Anisotripic magneto-resistive or AMR.
The magnetoresistive strips or elements may be formed into four separate legs of a Wheatstone Bridge. The legs are then oriented to be sensitive to a field perpendicular to the initial magnetization direction. Bridge configurations that conserve space include arrangements in which the four elements are provided in a single plane, in single columns or rows, or as two side-by-side sets of two elements each.
A magnetic field sensor also can be made of a Giant Magneto-resistive (GMR) thin film. A GMR film consists of multiple layers of ferromagnetic film that are separated by Noble metal or insulating compound films. The resistance of the GMR film depends on the relative magnetization angle between adjacent ferromagnetic layers.
A magnetic field sensor incorporating such magnetoresistive elements is sometimes formed on a semiconductor substrate using integrated circuit techniques, and the substrate is provided with an insulating layer, typically silicon dioxide and/or silicon nitride.
It is also known to use signal isolators to isolate input and output signals with a potential difference between their respective grounds. These signal isolators have been used in various fields, for example, in industry controls, in order to eliminate transient currents for safety purposes. Also, these signal isolators have been used in communication networks to provide high speed signal transmission with less noise.
A magnetic signal isolator usually includes a magnetic field sensor, such as one or more of the magnetoresistors, and an input coil. The input coil is coupled to the input of the magnetic isolator in order to generate a magnetic field in response to an input signal. The magnetic field sensor senses this magnetic field and produces a corresponding output signal. Accordingly, the input coil receives an input signal from a first circuit operating at a first voltage level, and the magnetic field sensor responds to the magnetic field by producing an output signal in a second circuit operating at a second voltage level, which may be either lower or higher than the first voltage level, and which may have an ground reference voltage isolated from the inputs.
However, typical magnetic sensors have limited signal ranges and linearities that can limit performance, especially in the case of linear magnetic signal isolators.
The present invention offers an integrated magnetically coupled signal isolator that effectively uses closed-loop feedback architecture to improve isolator linearity, signal range, and immunity to uniform external magnetic fields in any direction.
In accordance with one aspect of the present invention, an integrated circuit signal isolator having a plurality of layers formed over a substrate comprises a magnetic field sensor, an input coil, feedback coil, and dielectric layers. The magnetic field sensor is formed in a first of the plurality of layers, the input coil is formed in a second of the plurality of layers, and the feedback coil is formed in a third of the plurality of layers. The feedback coil is coupled to an output of the magnetic field sensor. The dielectric layers separate the magnetic field sensor, the input coil, and the feedback coil.
In accordance with another aspect of the present invention, an integrated circuit signal isolator comprises a semiconductor substrate, a sensor metal layer, an input coil metal layer, a feedback coil metal layer, and dielectric layers. The sensor metal layer contains a magnetic field sensor that provides an output signal corresponding to an input signal of the integrated circuit signal isolator. The input coil metal layer contains an input coil that receives the input signal of the integrated circuit signal isolator. The feedback coil metal layer contains a feedback coil, and the feedback coil is coupled so as to receive a signal based on the output signal from the magnetic field sensor. The dielectric layers separate the sensor metal layer, the input coil metal layer, and the feedback coil metal layer.
In accordance with a further aspect of the present invention, a method for providing closed loop linear signal isolation comprises the following: converting an input signal to a first magnetic field by use of a first coil integrated on a single chip; converting the first magnetic field to a sensor electrical output signal by use of a magnetic field sensor integrated on the single chip; and, converting the sensor electrical output signal to a second magnetic field by use of a second coil integrated on the single chip, wherein the second magnetic field is arranged to cancel the first magnetic field.